Why Ivanka Trump won't be voting for her father in the New York primary...

In the New York Republican primary on April 19, Ivanka Trump will be casting her ballot for … nobody! Yes, not even her father, GOP frontrunner Donald Trump.

Donald told Fox & Friends on Monday that his son Eric won't be voting for him either, but there's a simple (and somewhat unbelievable) reason for that: both missed the voter registration deadline.

Score one (actually two!) for Ted Cruz.

"They had a longtime register and they were, you know, unaware of the rules, and they didn't, they didn't register in time," the former "Celebrity Apprentice" host said. "They feel very guilty, but it's fine. I understand that. I think they have to register a year in advance and they didn't. So Eric and Ivanka, I guess, won't be voting."

He joked that he was going to cut off their allowance for the oversight.

To vote in the New York primary, voters must register and choose their party affiliation several months in advance.

Both Ivanka and Eric (both of whom starred in "Celebrity Apprentice" with Donald) have campaigned alongside their father, so their allegiance isn't in doubt.

For Ivanka, it's a little more understandable about why she missed the registration, as she announced that she was pregnant with her third child around the deadline.

On March 27, she and her husband, Jared Kushner, welcomed son Theodore James. It's the eighth grandchild for Donald.

"Jared and I feel incredibly blessed to announce the arrival of Theodore James Kushner. Xx Ivanka," she tweeted after the birth to her 840,000 followers.

After her son came into the world, she also posted a snap of her holding her bundle of joy while saying, "My heart is full." Just 48 hours after the birth, Ivanka returned to her luxurious New York apartment while looking incredible in a red floral Dolce&Gabbana dress.

On April 10, the mother of three posted a sweet snap on Instagram of her daughter Arabella cradling her newborn son on National Sibling Day.

Along with the cuddly pic of the siblings, the 34-year-old wrote, "Sunday morning cuddles."